Fix potential stack underflow in mpi_read_file.
When provided with an empty line, mpi_read_file causes a numeric
underflow resulting in a stack underflow. This commit fixes this and
adds some documentation to mpi_read_file.
diff --git a/ChangeLog b/ChangeLog
index fe5ce65..ecbacef 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
mbed TLS ChangeLog (Sorted per branch, date)
+= mbed TLS x.x.x branch released xxxx-xx-xx
+
+Bugfix
+ * Fix potential stack underflow in mpi_read_file.
+ Found by Guido Vranken.
+
= mbed TLS 2.1.7 branch released 2017-03-08
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